An ultrasonic probe comprises a plurality of piezoelectrics. Moreover, electrodes are arranged on both sides of the piezoelectronics such that they interleave the piezoelectronics. There are various ways of guiding electrodes regarding the piezoelectronics. For example, one method involves conducting electrodes arranged in front surface, which is the surface of the ultrasonic radiation direction side of the piezoelectrics, with FPC (Flexible Printed Circuits). Signals derived from FPC are transmitted to a transmitter-receiver circuit.
Generally, the acoustic impedance of body tissues is approximately 1.5 Mrayl. Moreover, the acoustic impedance of piezoelectrics is 30 Mrayl or more. In other words, there is a large difference in impedance between body tissues and piezoelectrics. Therefore, acoustic mismatching occurs when body tissues are directly contacted to piezoelectrics. As a result, ultrasonic beams are reflected at borders with greatly different acoustic impedance. Accordingly, an acoustic matching layer is necessary between body tissues and piezoelectrics. The acoustic matching layer is an intermediate layer that efficiently propagates ultrasonic waves.
Moreover, in order to reduce and alleviate the acoustic mismatching mentioned above, a plurality of acoustic matching layers is sometimes configured. In the configuration, a plurality of acoustic matching layers with different acoustic impedance between the acoustic impedance of the body tissue (for example, 1.5 Mrayl) and the acoustic impedance of piezoelectrics (for example, 30 Mrayl) is gradually layered.
In the configuration, for example, if the acoustic impedance of first layer in the acoustic matching layer is approximately 9 to 15 Mrayl, a machinable ceramic is used as a material with such acoustic impedance. Machinable ceramics are mainly composed of mica and are non-conductive material.
Here, a driving voltage must be applied to the piezoelectrics in order to transmit ultrasonic waves. The electrode provided to the piezoelectrics and the driving circuit of the ultrasonic diagnostic equipment are connected using cables, etc., in order to apply the driving voltage. Moreover, when receiving ultrasonic waves, the received signals must be extracted from the piezoelectrics. In order to extract the received signals, the electrode of the piezoelectrics and the driving circuit of the ultrasonic diagnostic equipment are connected using cables, etc. As a principle measure for electrically connecting with piezoelectrics, one method uses an electrode pattern formed on substrates with relatively small acoustic impedance. FPCs are mainly used as the substrate. However, mismatching occurs when the FPCs are directly connected to the electrode of the piezoelectrics. For example, if the acoustic impedance value of the FPCs is approximately 3 Mrayl, as mentioned above, nonconformity of the acoustic impedance occurs between the body tissues and the piezoelectrics. Accordingly, the FPCs must be established via several acoustic matching layers mentioned above. When arranging the non-conductive acoustic matching layer on the first layer, the non-conductive acoustic matching layer is present between the electrode of the piezoelectrics and the electrode on the FPCs, consequently electrical connection is not performed. That is, a conductive path must be provided on the non-conductive acoustic matching layer.
For example, in a two-dimensional array ultrasonic transducer, electrodes must be derived to the FPCs from each of a huge number of elements. Accordingly, in conventional ultrasonic transducers, a through hole is formed with respect to the non-conductive acoustic matching layer, the through hole comprising electric conductivity provided in correspondence with the number and arrangement of the piezoelectrics in the layering direction. In the ultrasonic transducer, the same number of through holes as the piezoelectrics is formed on the acoustic matching layer, and the conductive path is secured by, for example, plating the entire surface of the through holes.
Moreover, in the conventional manufacturing method of ultrasonic transducers, a conductive film is provided on both surfaces of the board of the non-conductive material, and the acoustic matching layer is formed by overlapping both surfaces of the conductive film of the board thereof. That is, the non-conductive material formed by overlapping the surfaces of the conductive film of the board comprises the conductive path toward the layering direction. As an example, a board of non-conductive material having the same width as the pitch of piezoelectrics is formed, with the conductive film provided on both surfaces thereof. The boards are overlapped in a number corresponding to the number of columns or rows of the piezoelectrics to form several blocks. Furthermore, the blocks are further overlapped to form the acoustic matching layer. In the acoustic matching layer formed by the process, the board and a superposed plane of the board function as the conductive path of the electrode and the FPC.